The present invention relates to a sheet feeder for separating a sheet from stacked sheets in a sheet storage cassette and for feeding the sheets one by one to a printing mechanism of a printer, a copying machine, a typewriter or the like.
A conventional sheet feeder as disclosed in U.S. Pat. No. 4,438,915 includes a sheet storage cassette (sheet hopper) which stores the stacked cut sheets and feed rollers which feed out one of the cut sheets out of the sheet storage cassette. The sheet storage cassette is provided with a hopper plate on its inside bottom. The hopper plate is urged by a spring so as to press the stacked sheets toward the feed rollers. The uppermost sheet of the stacked sheets is therefore constantly pressed on the feed rollers. A pair of separator pawls are provided on both corners of a sheet exit side of the sheet storage cassette. When the feed rollers are rotated, the uppermost sheet is bent and deflected between the pawls and the feed rollers. Owing to the deflection of the uppermost sheet, a restoration force of the uppermost sheet occurs and the sheet rides beyond the separator pawls. Thus, the uppermost sheet is separated from the stacked sheets and is fed out of the sheet storage cassette.
The conventional sheet feeder separates the uppermost sheet from the stacked sheets by utilizing flexibility and restorativeness of the sheet, as described above. Accordingly, the conventional sheet feeder cannot deal with thick sheets, e.g., post cards, envelopes and the like which lack of the flexibility and the restorativeness. In other words, the conventional sheet feeder cannot feed the thick sheets one by one to the printing mechanism.